JP2021500729A - Electronic source - Google Patents

Abstract

From an electron emitting cathode, which is an electron source in a gas source mass analyzer and presents a thermionic emission surface to communicate with the gas source chamber of the gas source mass analyzer and provide electrons to it, and an electron emitting cathode. Heating that is electrically insulated and is arranged to be heated by the current in it and to radiate enough heat to the electron emitting cathode to thermoelectronly release electrons from the electron emitting surface. An electron source that comprises an element and uses it to provide a source of electrons for use in ionizing the gas in the gas source chamber. [Selection diagram] Fig. 3

Description

Detailed description of the invention

[Field]
[01] The present invention relates to an electron source for providing electrons in a mass spectrometer, such as a gas source mass spectrometer.

[background]
[02] Many scientific instruments rely on the ionization of gas molecules to prepare the molecules for later manipulation. Electron beam impact is commonly used in this process. The electrons are generated by thermionic emission from the cathode, and these electrons are accelerated through the amount of gas molecules contained, and the collision between the electrons and the gas molecules ionizes a certain percentage of the molecules.

[03] Conventional ion sources typically use tungsten filaments arranged in various geometric arrangements (eg, ribbons, coiled wires), in which case the filaments also act as cathodes and the electrons are their. Emitted from the surface. However, while this design is easy to manufacture, it has significant drawbacks that limit its performance. These drawbacks include, but are not limited to:

Mechanical instability
[04] The heated filament is self-supporting and is prone to change in shape. This can result in significant variations in the behavior of the source, which can jeopardize the data and require the source to be opened for repair work.

Potential gradient
[05] It is important that the cathode operates at a uniform and stable voltage in order to suppress the energy of thermionically generated electrons to a narrow energy band. The heating wire cathode has a unique voltage gradient along its length due to the heating current. Therefore, the applied voltage is not constant as it must be adjusted to maintain radiation at the required intensity.

Operating temperature
[06] The high work function of these heated filaments requires a high operating temperature that promotes the formation of hydrocarbon volatiles that interfere with the gas species under investigation (ie, provided by electron-based ionization).

Limited emission current
[07] A relatively low emission current achievable using this technique limits the ionization rate, thereby limiting the sensitivity of the instrument using it. This requires the user to constantly evaluate the sensitivity, operating temperature and time between repairs of the instrument.

Limited lifespan
[08] Significant efforts are required to establish acceptable operation of such electron sources in most vacuum instruments. Operating the heated filament / cathode of the electron source at a higher temperature shortens the filament life, resulting in excessive filament service / replacement downtime.

[09] The present invention aims to address one or more of these defects.

[Overview]
[10] The present invention is an alternative cathode configuration in which the electron emitting cathode is heated by a filament electrically insulated from the cathode. Most preferably, the cathode is placed on a gas source mass spectrometer or other gas source instrument for generating ionized gas for analysis. One example is the so-called Nier source mass spectrometer.

[11] In a first aspect, the present invention provides an electron source in a gas source mass analyzer, for the electron source to communicate with and provide electrons to the gas source chamber of the gas source mass analyzer. The electron emitting cathode, which presents a thermionic emission surface, is electrically isolated from the electron emitting cathode so that it is heated by the current inside, and the thermionic release of electrons from the electron emitting surface. It comprises a heating element arranged to radiate sufficient heat to the electron emitting cathode, which is used to provide a source of electrons for use in ionizing the gas in the gas source chamber.

[12] In this way, it is not necessary to pass the electric heating current through the electron emission surface. Instead, the electric heating current electromagnetically transfers heat to the electron-emitting cathode, which is positioned next to the heating element, so that it can absorb the radiated heat energy and heat it remotely. In order to radiate, it is passed through a separate heating element that is heated to a sufficient temperature, for example to the incandescent heat. Eliminating the need to apply a voltage across the directly electrically heated electron emission coil avoids the problems associated with the potential gradients described above and the resulting fluctuations in emitted electron energy. .. This provides a more homogeneous electron energy, which allows greater control over the conditions that affect the ionization probability within the source (narrowing of ΔE ₂ , FIG. 8B).

[13] Furthermore, the separation of the electroheating and electron emitting modes of the electron source in the present invention allows the use of much more optimal materials for thermionic emission that are not suitable for electrical heating. .. In fact, electron emission has been found to increase up to 5-10 times compared to the rate of electron emission from existing electrically heated electron sources that operate for comparable operating lifespans. Therefore, it is possible to increase the electron emission rate from existing electrically heated electron sources, but the significant cost is that the electrically heated sources "burn out" very quickly. is there. It then requires replacement within the mass spectrometer, which requires the spectrometer to be opened (vacuum is lost), possibly resulting in months of rest. Compared to existing systems, the present invention has shown that higher electron emission rates can be achieved at significantly lower operating temperatures. This has remarkable actual results, as the reduction in temperature reduces the presence of hydrocarbon volatiles in the vacuum of the mass spectrometer in use. As discussed above, these hydrocarbon volatiles can be ionized in the gas source chamber and become the resulting ions that interfere with the isotope species of interest, which we study. Mass spectrometers may be used for this purpose.

[14] For example, the flow rate of electrons into or throughout the gas chamber can exceed 500 μA, preferably more than 750 μA, or more preferably more than 1 mA, or 2 mA. It is even more preferable to be able to exceed. For example, the electron flow rate may be between 500 μA and 1 mA, or between 1 mA and 2 mA. These electron flow rates are preferably less than 2000 ° C., such as when the temperature of the electron emitting cathode is between 750 ° C. and 1000 ° C., more preferably less than 1500 ° C., or less than 1250 ° C. It may be achievable even more preferably, or even more preferably below 1000 ° C. For example, a gas source mass analyzer can be equipped with an electron trap that can operate to receive electrons from the electron emitting cathode, which causes the electron emitting cathode to be heated to a temperature of 2000 ° C. or lower by a heating element. In response, it traverses the gas source chamber with a current of at least 0.5 mA.

[15] The gas source chamber is to receive electrons from the electron emitting cathode at an electron input opening shaped to form an electron beam in the gas source chamber directed towards the electron trap without the use of a collimator magnet. Can be placed. This is due to the significantly higher electron flow rate achievable by the present invention. Embodiments of the invention can include collimator magnets, if desired, but use collimator magnets to increase electron beam intensity (ie, flow rate per unit area in the lateral direction with respect to the beam). It turns out that collimation is no longer needed. According to the present invention, sufficient electron beam intensity can be achieved by improving the electron flow rate.

[16] The electron source can include an energy controller arranged to control the energy of the electrons output by the electron source. The energy controller can include an anode disposed between the thermionic emission surface and the gas source chamber. The energy controller can include a control device arranged to apply a variable potential to the anode to accelerate the electrons emitted from the thermionic emission surface in the direction towards the gas source chamber. The energy controller can include one or more electron extraction grids disposed between the thermionic emission surface and the gas source chamber. The control device is arranged to apply an electric potential to the electron withdrawal grid to attract the emitted thermions towards the grid. The grid is capable of passing thermoelectrons from the electron source and is reticulated or porous, or otherwise, the thermions attracted to the electron-drawing grid make the electron-drawing grid a thermoelectron emitting surface. It is preferable that a through hole arranged so as to communicate with the thermionic emission surface is provided so that the side surface facing the thermoelectron can pass through the side surface facing the gas source chamber. The anode is preferably located between the gas source chamber and the side surface of the electron extraction grid facing the gas source chamber. This allows the anode to accelerate thermions that have passed through the electron drawing grid towards the gas source chamber. The energy controller can include one or more electron focusing electrodes disposed between the thermionic emission surface and the gas source chamber and in parallel with the anode. One or more focusing electrodes can define or include, for example, an Einzel lens, or other ionic optical lens arrangement. One or more electron focusing electrodes may be arranged between the anode and the gas source chamber so as to focus thermions from the thermionic emission surface into the gas source chamber via the inlet to the latter. it can.

[17] The improved emission rate of electrons from the electron emission cathode for a given temperature of the heating element is sufficient compared to existing electron emission systems that employ electrically heated electron emission services / materials. It has been found that electron emission rates can be achieved at lower power input levels. For example, the electron emitting cathode may be operable to be heated by the heating element to a temperature of 2000 ° C. or lower when the power input to the heating element does not exceed 5 W. The power input preferably does not exceed 4W, more preferably does not exceed 3W, even more preferably does not exceed 2W, or even more preferably does not exceed 1W. The power input to the heating element may be between about 0.5W and about 1W. These lower power input ratings allow the electron source to last longer with a lower cathode degradation rate, allow operation at lower temperatures, and all of the associated benefits emerge from it. .. A lower cathode degradation rate results in improved electron output uniformity, which improves electron source consistency. For example, the relatively high degradation rates of existing electrically heated electron emitting cathodes result in inconsistent cathode performance and mechanical instability. Because the cathode physically loses material during use (“burns out”), thereby often gradually changing its shape, especially in response to heating, which has the effect of altering electron output performance. Because it has. These problems are significantly reduced according to the present invention.

[18] The electron emitting cathode can be selected from an oxide cathode, an I cathode or a Ba impregnated cathode. The electron emitting cathode can include a base carrying a coating of thermionic emitting material that presents an electron emitting surface. When the electron emitting cathode comprises a base carrying the coating, the coating can include a material selected from alkaline soil oxides, osmium (Os), ruthenium (Ru). The work function of the electron emission surface at a given temperature can be reduced by the presence of the coating. For example, the coating material can provide a work function of less than 1.9 eV at temperatures below 1000 ° C. When no coating is used, the work function of the electron emitting surface may be greater than 1.9 eV at temperatures below 1000 ° C. Many other types of possible release material (e.g., tungsten, W, yttrium oxide, for _example, Y 2 _{O 3,} tantalum, Ta, lanthanum / boron compound, e.g., LaB ₆₎ is available.

[19] The base can comprise tungsten or nickel. The base may be a metallic material that separates the coating from the heating element.

[20] Oxide cathodes are generally cheaper to produce. They can be equipped with, for example, a spray coating with carbonic acid (Ba, Sr, Ca) particles or carbonic acid (Ba, Sr) particles on a nickel cathode base. This results in a relatively porous structure with a porosity of about 75%. The spray coating can include rare earth oxides, such as dopants such as Europia or yttria. These oxide cathodes provide good performance. However, other types of cathodes that may be robust due to exposure to the atmosphere (eg, when the mass spectrometer is opened) can be employed.

[21] The so-called "I cathode" or "Ba impregnation" can include, for example, a cathode base made of porous tungsten impregnated with a barium compound, having a porosity of about 20%. The base can comprise tungsten impregnated with a compound containing barium oxide (BaO). For example, tungsten is 4BaO. CaO. It may be impregnated with Al ₂ O ₃ or other suitable material.

[22] The electron source can include a sleeve that surrounds the heating element, with an electron emitting surface at the end of the sleeve.

[23] The heating element can comprise a metal filament coated with a coating with a metal oxide material.

[24] In another aspect, the invention can provide an ion source for a mass spectrometer equipped with the electron source described above. The ion source may be a gas source (of ions), for example, a Nier type gas source, for example, a Nier type rare gas ion source.

[25] In yet another aspect, the invention can provide a mass spectrometer with a gas source (of ions), as described above. The gas source of the mass spectrometer may be a gas source, for example, a Nier type gas ion source, for example, a Nier type rare gas ion source.

[26] In another aspect, the invention can provide a gas source mass spectrometer with an electron source, as described above, in which case the gas source is an electron from the electron source into the gas source chamber. An electronic input port for receiving, and an electron source and an electronic input port for entraining / directing electrons from the electronic source toward the electronic input port (for example, collimating or converging toward the electronic input port). It has a gas source chamber with an electro-optical part arranged between the two. The electro-optical portion may be an electro-optical lens such as an electrostatic lens (eg, including one or more Einzel lenses). The electron optics portions are disposed away from the gas source chamber and can be spaced from it by a distance of at least 1 cm, or at least 1.5 cm, or at least 2 cm, or at least 2.5 cm. The optical axis of the electron optics portion may be coaxial (or at least aligned with) the center of the electron emission surface of the electron source. The electron emission surface may be substantially flat. The optical axis of the electro-optical portion may be coaxial (or at least aligned with) the center of the electronic input port. The electro-optical portion is provided with a through opening or hole through which electrons can be transmitted from the electron source. The diameter or width dimension of the through opening or hole may be substantially the same as or larger than the diameter or width dimension of the electron emitting surface. In this way, since the electrons are emitted into the holes of the electron optics portion, it is possible to present and clarify substantially the entire electron emitting surface.

[27] The electron optics portion comprises one or more electrodes (eg, lens rings) arranged to receive one or more voltages, which are used to electron the electrons emitted from the electron source. An electric field configured to urge / direct (eg, collimate or converge) towards an input port can be generated. The electron optics portion can be arranged to urge / direct electrons from the electron source to form a beam of electrons converging towards a region of minimum beamwidth arranged in the gas source chamber. The gas source mass spectrometer includes a control device arranged to apply the one or more voltages (eg, an adjustable voltage value) in an adjustable manner, and uses the control device to apply the minimum beam width in the gas source chamber. The position of the area can be adjusted.

[28] The gas source mass spectrometer preferably has no magnets arranged to apply a magnetic field (eg, an electronic collimating magnet) over the entire gas source chamber. Therefore, the magnetic collimation of electrons from the electron source may be absent. Electron optics can be achieved using an electro-optical part if it is optionally desired.

[29] The Nier-type mass spectrometer, initially designed by Alfred Nier, is a class of well-known mass spectrometers that form the ions of the sample of interest and the sources of those ions. An electric ion accelerator / optical device for forming a direct beam, a magnetic sector device for separating ions in the ion beam into a plurality of ion beams according to their mass-to-charge ratio (m / z), and each ion beam. It is equipped with an ion collector for measuring the current inside. A Nia-type mass spectrometer operates by ionizing a target gas sample (for example, a rare gas) in what has become known as a Nia-type gas ion source and accelerating the ions from the ion source through a potential difference of several kV. To do. Accelerated gas ions are separated in motion by directing the field lines perpendicular to the ion orbit and passing them through the sector magnetic field region. The resulting beam of ions is separated by a magnetic field due to the mass-to-charge ratio (m / z) of the ions. Beams with lighter ions bend with a smaller radius in the sector magnetic field region than beams with heavier ions. The current of each ion beam is then measured using a "Faraday cup" or a photomultiplier tube detector. The present invention has, but is not limited to, specific applications for Nier-type gas ion sources and Nier-type gas ion mass spectrometers.

[30] Examples of studies on the structure and performance of common Nia-type gas ion sources include "Mapping changes in helium sensitivity and peak shape for variing parameters of Nier-type noble gas". Written by J. Anal. At. Spectron. , 2012, 27, 1012 (DOI: 10.1039 / c2ja10339g). This illustrates the existing prejudice of using direct heat (ohm-like) filaments as a source of electrons in the Nier gas source design. Another example of this prejudice is "Applications of Organic Mass Spectrometery", John R. et al. De Laeter, Chapter 1.3.2, Fig 1.8, p. Found in 22, in which the schematic shows only such direct heat filaments. In addition, "Geochronology and Thermochronology by the 40Ar / 39Ar Method", Ian McDougall & T.I. By Mark Harrison, in Chapter 3.17.3, "Ion Sources" p. 78 explains that "... the electrons generated by thermionic emission from the thermal filament are most commonly made of tungsten ...". Book "Potasium-Argon dating: Principles, Technologies and Applications to Geochronology" G.M. Brent Dalrymple & Marvin A. Lanphere, in chapter 5, under the heading "Argon meter, Mass spectrometers, Ion source," on page 70, "... in an electron shock ion source, electrons are generated by filaments, and the filaments are generally tungsten ribbons or wires. …"It has said.

[31] The present invention opposes this predominant prejudice in the art.

[32] To gain a deeper understanding of the present invention and to show how its embodiments can be put into practice, then, by way of example only, reference is made to the accompanying diagram.

It is a figure which shows schematicly the tungsten filament coil electron emitter of the prior art. It is a figure which shows schematic the ion source of the gas source mass spectrometer which adopted the electron emitter of FIG. 1A. It is a figure which shows typically the electron source of the preferable embodiment of this invention. It is a figure which shows schematic the ion source of the gas source mass spectrometer which adopted the electron source of FIG. It is a plot showing the trap current (“ionization” current) generated by the existing electrically heated filament technology (see FIG. 1B) as a function of filament temperature. Note that there is no stable emission region over the entire temperature range. It is a drawing according to the embodiment of the present invention (see FIG. 3) that shows the trap current (“ionization” current) generated by the radiantly heated filament as a function of the heated filament temperature. It should be noted that the same emission level is achieved for the filament of FIG. 4, but at a much lower temperature and there is an additional region of stable emission at its 800 mA operating current. FIG. 5 is a graph showing FIGS. 4 and 5 together on the same scale to clarify very different operating characteristics and temperatures of operation. It is a figure which shows schematic the ion source of the gas source mass spectrometer which adopted the electron source of FIG. FIG. 5 is a graph schematically showing the distribution of thermionic energy from the types of heated coil electron sources shown in FIG. 1A. It is a graph which shows roughly the distribution of thermionic energy from the heated coil electron source of FIG. Schematically distributes the number of target / sample gas ions (per thermoelectrons, per cm of electron transfer, per mmHg of gas pressure) generated by a gas source mass spectrometer, plotted as a function of thermionic energy. It is a graph which shows. FIG. 5 is a graph showing data obtained using the present invention exemplified in the embodiments described herein, applied to an argon gas sample. FIG. 5 is a graph showing data obtained using the present invention exemplified in the embodiments described herein, applied to an argon gas sample. It is a front view of the result of the numerical simulation of the Nier type source, and the electron source adopted in the Nier type source is a direct heat filament coil as an electron source with and without an electron collimation magnet (not shown). It is the conventional Nier type source design adopted. It is a side view of the result of the numerical simulation of the Nier type source, and the electron source adopted in the Nier type source is a direct heat filament coil as an electron source with and without an electron collimation magnet (not shown). It is the conventional Nier type source design adopted. It is a front view of the result of the numerical simulation of the Nier type source, and the electron source adopted in the Nier type source conforms to the present invention, and is a direct heating coil with and without an electron collimation magnet (not shown). Not a filament. It is a side view of the result of the numerical simulation of the Nier type source, and the electron source adopted in the Nier type source conforms to the present invention, and is a direct heating coil with and without an electron collimation magnet (not shown). Not a filament. It is a front view of the result of the numerical simulation of the Nier type source design, and the electron source adopted in the Nier type source is in accordance with the present invention, both with and without the simultaneous use of the electron collimation magnet (not shown). , Einzel lens electron focusing arrangement is adopted. It is a side view of the result of the numerical simulation of the Nier type source design, and the electron source adopted in the Nier type source is in accordance with the present invention, both with and without the simultaneous use of the electron collimation magnet (not shown). , Einzel lens electron focusing arrangement is adopted.

[Explanation of Embodiment]
[48] FIG. 1A schematically shows a prior art electron source for a gas source mass spectrometer. The electron source is a tungsten wire filament coil 1 having each opposite wire end electrically connected to a current input terminal 4 having a first potential, and a current having a second potential different from the first potential. It includes an output terminal 5 and allows current to flow through the filament coil 1. Sufficient current flows through the tungsten filament coil to heat the surface of the filament coil to a temperature sufficient to thermoelectronly emit electrons from the surface (eg, emit light). That is, the thermal energy obtained by the electric thermal effect of the current passing through the filament coil is sufficient to pour electrons into the filament coil and obtain energy that exceeds the surface work function of the filament coil.

[49] Electrons are generally emitted from the filament coil 1 in all directions, but the electrons (3) emitted in the preferred direction are selected for input into the gas source chamber of the gas source mass spectrometer and are the gas source. The filament coil 1 communicates with the chamber via an electron input slit 2 formed on the side wall of the chamber in which the filament coil 1 is located adjacent to the chamber.

[50] FIG. 1B shows the structure of the gas source chamber of the gas source mass spectrometer using the filament coil 1. The gas source mass spectrometer includes a gas source block 7 in the wall, and an electron input slit 2 in the wall is formed adjacent to the filament coil 1 (outside the gas source block). The electrons emitted by the filament coil 1 are attracted towards the gas source block 7 by the potential difference (negative with respect to the source) used to accelerate thermions to the desired energy. The electron potential is the potential difference (expressed in volts) between the filament and the gas source block. Its role is dual, with the direction of the potential field accelerating the electrons towards the gas source block, but the magnitude of the potential provides enough energy to cause an ionization event.

[51] The electrons pass through the slit and enter the room of the gas source block as an ionizing electron beam of the source gas injected into the gas source block (gas injection means, not shown). The electrons from the electron beam 6 are formed on the wall of the gas source block, pass through the electron output opening 15 facing the electron input opening, and then are collected on the opposite side. The electrons are so collected by the electron trap unit 9 which is maintained at a positive voltage with respect to the source block. This electron beam traverses the chamber of the gas source block along the beam axis located just behind the ion exit slit 10, so that the ions formed by the collision of electrons with the neutral source gas molecule are Y focused. The penetrating "pull-out" electric field created by the plate 11 can be efficiently pulled out of the chamber. The extracted ion beam is directed to an output slit 12 formed on a flat plate so as to collimate the ion beam 13 for further operation / use in the mass spectrometer.

[52] The ion extraction electric field is modified by the presence of the ion repulsion electrode plate 8 inside the source block chamber. The ion repulsion electrode plate is usually operated at a negative potential to ensure that gas ions are formed by the impact from thermions of the electron beam 6 in a region of relatively low electric field gradient. The ionized electron beam 6 is restricted in its passage between the filament coil 1 and the electron trap unit 9 due to the presence of two collimating magnets 14 that generate a magnetic field of more than 200 gauss parallel to the required electron beam axis. To. This magnetic field also serves to increase the probability of collision of the gas with atoms / molecules and the path length of the electrons that increase their ionization. The ions drawn from the ionization region pass between the Y focusing plates 11 and are carried so as to be focused in the region of the demarcation slit 12. The formed image is usually smaller than the width of the slit 12. This reduces mass discrimination at the source due to the presence of a magnetic field from the source magnet.

[53] Nier-type gas ion sources are commonly used as ionization sources in gas mass spectrometers. Nier-type gas sources are arranged to ionize neutral gas atoms or molecules by causing them to collide with electrons, as shown in FIGS. 1B, 3 and 7. In particular, electron streams are generated and directed into the analytical sample of gas atoms or molecules, thereby ionizing them. The heated filament is maintained at a negative voltage (typically -50 to -100 V) with respect to the ionization chamber so as to accelerate the electrons from the filament towards the ionization chamber. The energy of the source electron is high enough to remove the electron from the neutral gas atom / molecule of the analytical material. The ions thus generated are pushed / pulled in a direction perpendicular to the path of the ionized electron beam by two sets of plates known as "half-plane" 11 and "zero-plane" 12. The hemiplane is maintained at a voltage that is typically about 85% of the gas source block 7.

[54] The rest of the mass spectrometer in which the apparatus of FIG. 1B forms an ion source is not shown or discussed herein, but employs an electrically heated electron source filament. A detailed example of such a gas source mass spectrometer is described in US Pat. No. 2,490,278 (AOC Nier) and further in the following paper with reference to FIG. To.

[55] "A Mass Spectrometer for Isotope and Gas Analysis", Alfred O. et al. Nier. The Review of Scientific Instruments, Volume 16, NUMBER 6, page 398, June 1947.

[56] It is desirable to increase the sensitivity of the mass spectrometer by producing more ionized electrons, which results in increased accuracy of the ion beam signal being measured. Mass spectrometers can be used to accurately measure ion beam currents. The limit of accuracy is controlled by the magnitude of the ion beam current with respect to the noise level of the system. Larger ion beam currents produce higher signal-to-noise ratios and therefore more accurate data. A larger ion beam is achieved by successfully ionizing more samples, and therefore the presence of more electrons contributes to this increased ionization. The tungsten filament 1 emits electrons by thermionic emission. Higher temperatures mean higher electron yields, which significantly reduces filament lifetime and increases local temperature in the source region. This can lead to more widespread interference with volatile hydrocarbons.

[57] The standard operating condition of a mass spectrometer requires that a stable thermionic beam current be measured by the electron trap unit 9. The magnitude and intrinsic stability of the electron trap current determine the magnitude and stability of the ion beam. The tungsten filament is operated by passing an electric current through a wire, and the current required to achieve a typical operating electron trap current of 200 μA is driven at 2.5 V and is approximately 2.4 A (total output approximately 6 W). Is. Tungsten filaments typically operate at approximately 2000 ° C. to obtain the required release.

[58] A mass spectrometer according to an embodiment of the present invention is shown in FIG. It differs from the arrangement of FIG. 1B in that the tungsten coil filament is replaced with the cathode filament 20 (partial cross section) schematically shown in FIG. Note that the arrangement shown in FIG. 3 does not include the collimating magnet 14 of FIG. 1B. This is due to the significantly higher electron flow rate achievable according to the present invention. Although it has been found that collimation using collimator magnets to increase electron beam intensity (ie, flow rate per unit area in the lateral direction with respect to the beam) is no longer necessary, embodiments of the present invention , If desired, a collimator magnet can be included. According to the present invention, sufficient electron beam intensity can be achieved by improving the electron flow rate.

[59] The operation of the apparatus of FIG. 3 is otherwise the same as that of FIG. 1B, except for the operation of the cathode filament 20 described below with reference to FIG. 2 and the lack of the collimating magnet 14. is there.

[60] The cathode filament electron source 20 comprises a separate heating element 24 and a cathode surface 26.

[61] The electron source includes electron emitting cathodes (25, 26) that communicate with the gas source chamber 7 of the gas source mass spectrometer and present a thermionic emission surface 25 for providing electrons 6 to it. .. The heating element 24 is electrically isolated from the electron emitting cathodes (25, 26) and is sufficiently hot to be heated by the current in it and to thermionically release electrons from the electron emitting surface. Is arranged to radiate to the electron emitting cathode. As a result, a source of electrons 6 for use when ionizing the gas in the gas source chamber is obtained.

[62] The benefit of this arrangement is that the emission surface is exposed to a more uniform acceleration potential, resulting in a narrower electron energy width. Thus, most or all thermions are present in the same location or region within the accelerating potential, thus improving the homogeneity of thermions generated for use in ionizing the target gas.

[63] The electric heating current is not passed through the electron emitting surface 26. Instead, the electric heating current is heated to a sufficient temperature and passed through a separate heating element 24 that electromagnetically radiates heat (eg, IR radiation) to the electron emitting cathodes (25, 26). The cathode absorbs the radiated thermal energy and in response emits thermionic electrons.

[64] The flow rate of electrons in the electron beam over the entire gas chamber can exceed 500 μA. The flow rate of electrons in the electron beam over the entire gas chamber may be between 0.5 mA and 10 mA, for example, 1 mA or several mA. These electron flow rates may be achievable when the temperature of the electron emitting cathode is less than 2000 ° C., for example about 1000 ° C. The electron emitting cathodes (26, 25) can be heated to a temperature of up to 2000 ° C. by the heating element 24 when the power input to the heating element is less than 5W. In fact, the power input to the heating element 24 may typically be between about 0.5W and about 1W.

[65] The electron emitting cathodes (26, 25) are oxide cathodes. In other embodiments, an I-cathode (also known as a Ba-impregnated cathode) can be used. The I-cathode comprises a Ni base 25 carrying a coating of thermionic emission material 26 that presents an electron emitting surface. The coating comprises carbonic acid (Ba, Sr, Ca) particles or carbonic acid (Ba, Sr) particles on the nickel cathode base. The electron source 20 includes a nichrome sleeve 23 that surrounds the heating element 24. The electron emitting surface 26 and the base 25 are collectively present at the end of the sleeve. The base 25 forms a lid that encloses the tat end of the sleeve. The sleeve serves to concentrate the heat from the heating element on the base 25, which conducts heat to the ejector coating 26.

[66] The heating element comprises a tungsten filament 21 coated with an alumina coating. This provides electrical insulation between the heating current in the heating element and the electron emitting cathodes (25, 26).

[67] The present invention provides greater electron emission at lower temperatures compared to tungsten filaments. Typical operation requires 6.3V at 105mA, which is approximately 0.6W of output. The local temperature on the cathode is then about 1000 ° C. This results in an electron trap current of about 1 mA and a corresponding 5-fold increase in sensitivity of the resulting ion beam generated by electron impact ionization of the source gas via the electron beam 6. The life of the cathode filament 20 is estimated to be greater than 10 years, which far exceeds the normal operating life of the tungsten coil filament 1 when attempting to generate equivalent emission currents.

[68] Benefits of using a cathode as an alternative to tungsten filament 1 include:

[69] Higher electron emission: about 5-10 times, with a lifetime comparable to existing tungsten filament 1. The tungsten filament coil 1 can produce similar emissions, but the life until it needs to be replaced is significantly reduced. Filament replacement can optionally result in months of rest.

[70] Lower operating temperature: This reduces the presence of hydrocarbon volatiles in vacuum that are ionized and interfere with the isotope species of interest.

[71] Higher levels of emission: This means that the external magnetic field (magnet 14) can be removed. This avoids the unwanted effect of this magnetic field on the mass spectrometer. This tends to be non-linear over a given range of partial pressures of the sample / target material, allowing ion mass discrimination between isotopes.

[72] No voltage drop across the cathode: This cannot be avoided when using the tungsten filament coil 1. This results in a more homogeneous electron energy that provides greater control over sensitivity.

[73] Mechanical stability: This improves the consistency of the electron source and the ion sources that use it and avoids staging of operation during the life of the cathode.

[74] Life extension: The lower operating temperature and conservative design of the cathode 20 results in an extension of the useful life of the cathode, coupled with a low filament degradation rate.

[75] The results of the comparative test on the Nier source rare gas mass spectrometer are shown with reference to FIGS. 4-6. These show some of the benefits of an electron source of preferred embodiments of the invention, such as those shown in FIG. 3 when compared to existing systems, such as those shown in FIG. 1B.

[76] Figures 4-6 show the "trap current" as a function of cathode temperature. The trap current is a fixed ratio of the total emission of the cathode and is the magnitude of the number of electrons flowing through the ionized region in the source block 7 at the near source. The trap current was measured with high accuracy in closed loop control to stabilize the operating state at the source.

[77] FIG. 4 shows a plot of the trap current (“ionized” current) generated by an existing electrically heated filament technique (see FIG. 1B) as a function of filament temperature. Note that there is no region of stable emission over the entire temperature range. FIG. 5 shows a plot of trap current (“ionization” current) generated by a radiantly heated cathode according to an embodiment of the invention (see FIGS. 2 and 3) as a function of heating filament temperature. The same emission level is achieved for the filament of FIG. 4, but at a much lower temperature, and there is a region of stable emission at its 800 μA operating current. FIG. 6 is a graph showing FIGS. 4 and 5 together on the same scale to clarify very different operating characteristics and temperatures of operation.

[78] It can be seen in FIG. 6 that the cathode 20 produces an equivalent level of emission at a temperature of about 1000 ° C., which is lower than that of the tungsten filament 1. This is a significant step forward in reducing interference from thermally induced contaminants by suspended hydrocarbons in vacuum.

[79] To obtain the drawing of FIG. 4, the tungsten filament coil 1 was driven about 400% more violently than typically used (ie, the electron trap current is typically about 200 μA). The 200 μA electron trap current in the system of FIG. 1B has acceptable levels of sensitivity (higher electron densities increase ionization, allowing lower levels of sample to be detected) and longer life (higher filament currents). It provides a compromise to achieve (lowering filament 1 more rapidly). Some users of the system of FIG. 1B may operate their filaments 1 at very high temperatures to detect small samples and accept the cost and confusion of downtime to replace the filaments 1. The cathode 20 according to the invention can operate in the higher "plateau" region of its properties (eg, 800 μA in FIG. 5) for many years, thus providing high sensitivity without compromise in life. Achieve.

[80] FIG. 7 schematically shows an ion source of a gas source mass spectrometer that employs the electron source of FIG. This is a modification of the arrangement described with respect to FIG. 3 above.

[81] The electron source (20, 30, 31, 32) includes an energy controller arranged to control the energy of the electrons output by the electron source. The energy controller includes an anode (31) disposed between the thermionic emission surface of the cathode (20) and the gas source chamber. The energy controller is a control device (not shown) arranged to apply a variable potential to the anode in order to accelerate the electrons emitted from the thermionic emission surface of the cathode in the direction toward the gas source chamber. Including. An electron extraction grid (30) is arranged between the thermionic emission surface of the cathode (20) and the gas source chamber. The control device is arranged to apply an electric potential to the electron withdrawal grid to attract the emitted thermions towards the grid. The grid is heated from the electron source so that the thermions attracted to the electron-drawing grid are allowed to pass through the electron-drawing grid from its side facing the thermionic emission surface to its side facing the gas source chamber. It allows electrons to pass through and is therefore reticulated.

[82] The anode (31) is arranged between the gas source chamber and the side surface of the electron drawing grid facing the gas source chamber. This allows the anode to accelerate thermions that have passed through the electron drawing grid towards the gas source chamber. The energy controller includes an electron focusing electrode (s) defining an Einzel lens (32) arranged parallel to the anode between the thermionic emission surface and the gas source chamber. The Einzel lens is disposed between the anode (31) and the gas source chamber, and focuses thermoelectrons as an electron beam (6) from the thermionic emission surface into the gas source chamber via the inlet to the gas source chamber. Arranged like this.

[83] The energy controller to the gas source chamber by controlling the acceleration voltage (s) applied to the anode (31), the extraction grid (30), or both. Arranged to control the thermionic energy for input. This controllability allows the thermions emitted from the cathode (20) of the present invention as compared to the much wider corresponding distribution of kinetic energy between thermions emitted from conventional heated coil emitters. The relatively narrow width in the distribution of kinetic energy between them is particularly effective and beneficial in the present invention.

[84] FIG. 8A schematically shows the distribution of thermionic energy (40) from the type of heated coil electron source shown in FIG. 1A. This is a wide Gaussian distribution caused by non-uniform and variable voltage distributions along the length of the heated coil. The width ΔE ₁ (full width at half maximum (FWHM)) of this energy distribution is large, and thermions have a wide range of energies.

[85] FIG. 8B schematically shows the distribution of thermionic energy (41) from the heated coil electron source of FIG. This narrow distribution has a small width ΔE ₂ (FWHM) and thermions have only a relatively small range of energies. Results transfer, energy controller of the control apparatus, the center position of the energy distribution (E _0), to a different (e.g., lower) the central position (e.g., shifted the distribution 42 around the energy E _'0) It will be possible to adjust to make it. Therefore, the controller of the energy controller adjusts the position of the energy distribution of the thermionic output, thereby optimizing the efficiency / probability of the electrons and causing the ionization of atoms in the target / sample gas in the gas source chamber. It is possible to operate.

[86] FIG. 8C schematically shows the distribution (43) of the number of ions produced per thermoelectrons in the target / sample gas, per cm of electron transfer in the gas source chamber, and per mmHg of gas pressure in the gas. Shown. This ionization rate is plotted as a function of thermionic energy. As shown, the maximum ionization probability occurs at thermionic energy ( _Epeak ), which is a relatively low energy and extremely sharp peak. The ionization probability drops steadily and rapidly with respect to the thermionic energies above and below this peak energy. Certain benefits of the present invention, for example, so that the energy E _{'0 =} E _peak, electrons relatively narrow from the electron source (i.e., dense) thermionic energy distribution, include the maximum ionization probabilities The ability to position at or near the electron energy to be generated. The narrow distribution of thermionic energies (width ΔE ₂ ) makes it possible to better optimize the efficiency of ion generation.

[87] In gas source mass spectrometry, ions are formed at the source by the process of electron shock. This process uses energy electrons that interact with gas phase atoms / molecules to produce ions. Traditionally, the source of electrons used in this process electrically heats the filament, which in turn produces electrons by thermionic emission. The "emission current" is the total current emanating from the heating filament, but the flow of energy electrons that can pass through the gas sample and thus ionize the gas sample is often referred to as the "trap current".

[88] It is desirable to improve the sensitivity of the gas source mass spectrometer by making the process of ionizing the gas sample more efficient. Often, the amount of sample material may be small or very small, and it is advantageous to maximize the ionization of the sample. Sensitivity has traditionally been achieved by collimating an electron beam using a magnetic field applied throughout the device and / or by increasing the trap current (ie, more electrons to generate more ions). It will be improved.

[89] However, increasing the trap current requires heating the filament to ever-increasing temperatures. This reduces the life of the filament, which literally "boils and evaporates." In addition, an increase in filament temperature means that the device at the gas source is heated to an increasingly greater extent by the radiant heat from the filament, which releases "background species" from the material forming the device. Be promoted. That is, the material (eg, steel, aluminum, etc.) of the structural parts (eg, walls) of the gas chamber to which the energy electrons are directed to carry out the ionization process is released into the gas chamber when the gas chamber is heated. Always contains some absorbed alien species of atoms or molecules. These alien species contaminate the gas sample being analyzed and reduce the quality of the data obtained from the mass spectrometer.

[90] The present invention makes it possible to increase the trap current without compromising the lifetime of the electron source and without increasing the background level of the alien species.

[91] Figures 9 and 10 show data obtained using the present invention, exemplified in the embodiments described herein, applied to argon gas samples. The figure shows the lower background levels of contaminants provided by the preferred embodiments of the invention, compared to typical levels of sensitivity and background contaminant levels achievable using existing heated filament electron sources. It clearly shows the greater sensitivity achieved in conjunction with.

[92] In particular, using low operating temperatures of electron sources (eg, 0.6 W), sensitivities up to 7 mA / Torr have been achieved for argon gas samples for trap currents higher than about 1 mA (FIG. 9). ), which is only about ^1x10 -14 CCSTP to contaminants ( "mass 36") has a background concentration (Figure 10). These sensitivities and background densities are much better than the standard industry level (“standard specifications”) for such magnitudes. The life of the electron source is more than 3.5 years under these operating conditions. This is much longer than the expected lifetime of a typical heated filament electron source.

[93] Conventional Nier-type electron impact / ionized gas source devices typically employ a direct heat filament coil as the source of those electrons. Usually, as shown in FIG. 1, the cathode is, for example, a coil of small wires of tungsten, which is heated to thermionic emission temperature by the application of an appropriate electric current.

[94] The filament assembly applies a bias voltage and therefore the emitted electrons have sufficient energy to ionize the analyte gas molecule. The filament needs to be heated to a very high temperature (about 1400 ° C.) in order to generate sufficient electron emission. High filament temperatures, coupled with the need to position the filaments very close to the ionization region, result in higher source assembly temperatures, typically between 150 and 200 ° C. Increasing source assembly temperature increases outgassing of pollutant background species. In rare gas analysis where the instrument is in static vacuum, any increase in background species is observed in the mass spectrum, which is especially problematic when the background ions are at the same pressure as the analyte ions. Further problems can arise when the analyte molecule breaks its relationship with temperature-related processes.

[95] In a conventional Nier-type electron impact / ionized gas source, thermions are emitted from the heated filament coil in all directions and only a small portion is permeated into the ionized region of the gas source device. The efficiency of this process can typically be only a few percent of thermions that eventually enter the ionization region. Traditional Nier-type sources are collimating magnets placed around the ionization region to suppress thermionic orbitals and to increase the path length of the electron orbitals by inducing spiral electron orbitals. Has. Unfortunately, the magnetic field generated by the collimation magnets also affects the orbits of the ions of the analyte generated in the ionization region, which introduces the most noticeable and unwanted mass bias effect at the lower ends of the mass spectrum. This complicates the spectral analysis of the analyte in the mass-to-charge ratio spectrum.

[96] A voltage drop across the filament produces an electron beam with a corresponding electron energy width. The electron energy width may be transferred to the analyte ion in some cases, reducing the mass resolution of the instrument.

[97] In the present invention, the debonding of the surface of the cathode (electron emitting surface) from the heater allows the surface to be thin and flat. Virtually all parts (or most) of the electron emitting surface are at substantially the same potential in the electric field when placed in an electric field to accelerate emitted electrons away from the surface for analysis ionization. Can exist in. The effect is that the potential difference (acceleration voltage) received by each (or at least most) accelerating electrons is substantially the same. Therefore, they carry substantially the same energy when entering the ionized region of the device. In other words, the cathode voltage can be consistent over substantially the entire electron emission surface. This minimizes the energy width of the emitted electrons. In addition, electron source heaters no longer need to be driven by a DC voltage, and AC can be used where application examples require.

[98] To better demonstrate the advantages and benefits of the present invention when applied to a nier-type gas source device as compared to conventional nier-type gas sources, FIGS. 11-16 are according to embodiments of the present invention. , And further, the results of numerical simulation of the electron orbit in the Nier-type source of gas ions by the conventional Nier-type source design are shown.

[99] Direct Heat Coil Filament-With or without Magnetic Collimation

[100] FIGS. 11 and 12 are a front view (FIG. 11) and a side view of a conventional knee-type source design using a direct heat filament coil as an electron source, both with and without an electron collimation magnet (not shown). (Fig. 12) is shown. For better understanding, in each of FIGS. 11 and 12, the thermionic trajectories and magnets are fully active (ie, when the magnetic field of the collimating magnet is "off" (ie, zero magnetic field). , Temporarily switched to "on") shows the result. This is to show the collimating effect of the magnet of the conventional Nier type source design. The voltages applied to the elements of the simulated Nier-type source structure are as shown in Table 1.

[101] Electron orbitals were simulated. Five groups of 300 electrons were created in the simulation, each group using 1 eV of energy to make up the electrons, and the surface of the filament coil evenly spaced around a circle with a diameter equal to the coil diameter of the filament electrode. Arranged around. The filament coil axis extends conceptually perpendicular to the plane of pages 11 and 12 so that the circle of simulated electron emission positions represents one winding of the coil. The five groups of electrons were evenly spaced and distributed along the axis of the coil of the filament electrode. As shown in Table 2, estimates of the percentage of these electrons were obtained that were successfully transmitted end-to-end in the ionized region and terminated at the trap electrode.

[102] As expected, when no magnetic field is included in the simulation, the proportion of electrons emitted from the filament coil in all directions and transmitted through the gas source chamber and all the way to the trap electrode is very small. The application of a collimating magnetic field throughout the device in the simulation provides a level of electron beam suppression in addition to making the electrons follow a spiral path. The number of electrons transmitted through the trap electrode is approximately 10-fold higher when the collimating magnet is applied in this simulation than when the collimating magnet is not applied.

[103] Indirect Hot Cathode-With or without Magnetic Collimation

[104] FIGS. 13 and 14 show the results of numerical simulations, in which case the electron source employed within the Nier-type source is not a direct heating coil filament according to the present invention. The cathode portion of the electron emission surface of the electron source was positioned 1.5 mm from the inlet opening of the gas source chamber / housing. The voltage was applied as shown in Table 3.

[105] FIGS. 13 and 14 show a front view (FIG. 13) and a side view (FIG. 14) of a new Near-type source design with and without simultaneous use of electron collimation magnets (not shown). For better understanding, each of FIGS. 13 and 14 shows the electron trajectories in the absence of any collimating magnets (ie, zero magnetic field) and the results in the presence and full working of the magnets. .. This is to show the collimating effect of the magnet of the new Nia type source design.

[106] Electron orbitals were simulated for each electron in a group of 1500 electrons. Each electron was created using 1 eV energy and emitted from different points located on the electron emitting surface (cathode), evenly spaced around a circular 1 mm diameter on its surface. .. As shown in Table 4, an estimate of the percentage of electrons successfully transmitted through the trap electrode through the ionization region was made.

[107] Due to the planar nature of the emission surface of the electron emitter, and because it is oriented (facing) the inlet opening of the gas source chamber, a larger proportion of the emitted electrons is the gas source. It is transmitted to the trap electrode through the chamber. The level of electron transmission is very similar to that observed in the previous example (conventional Nier-type source) where the heated coil filament was used as an electron source in conjunction with a collimation magnet (slightly). good). The addition of the collimating magnetic field causes the electron beam to be suppressed and a larger proportion of electrons to be transmitted into and through the gas source chamber and reach the trap electrode, as expected. Has a mating effect. There is an approximately 3-fold increase in electron transmission compared to when no magnetic collimation is used.

[108] Indirect Hot Cathode and Einzel Lens-With and without Magnetic Collimation

[109] To simulate the addition of the Einzel lens to the new Nia-type gas source device, two coaxial separation lens ring electrodes were added to the device as shown in FIGS. 15 and 16. Each Einzel lens ring had an inner diameter (ID) of 1.5 mm, an outer diameter of 2.5 mm and a thickness of 0.5 mm. The distance between the electron emitting surface (cathode) and the first lens ring was 0.5 mm. The distance between the first lens ring and the second lens ring was 0.5 mm. The distance between the second lens ring and the opposing outer layer of the gas source chamber / housing (including the inlet opening) was also 0.5 mm. Voltages were applied to these components as shown in Table 5.

[110] FIGS. 15 and 16 show a front view (FIG. 15) and a side view (FIG. 16) of a new Near-type source design with and without simultaneous use of electron collimation magnets (not shown). For better understanding, each of FIGS. 15 and 16 shows the electron trajectories in the absence of any collimating magnets (ie, zero magnetic field) and the results in the presence and full working of the magnets. .. This is to show the collimating effect of the magnet of the new Nia type source design.

[111] Electron orbitals were simulated for each electron in a group of 1500 electrons. Each electron was created using 1 eV energy and emitted from different points located on the electron emitting surface (cathode), evenly spaced around a circular 1 mm diameter on its surface. .. As shown in Table 6, an estimate of the percentage of electrons successfully transmitted through the trap electrode through the ionization region was made.

[112] As clearly shown in the figure, the focusing / focusing effect is imposed on the orbit of the emitted electrons by using the Einzel lens. A small change in the voltage applied to the first Einzel lens ring (lens 1) has the effect of moving the focal point (or the maximum convergence point of the electron beam) from the cathode closer or further away as needed. Has. The voltage values shown above were selected so that the focus was approximately in the center of the gas source chamber of the source enclosure.

[113] The ions generated by the energy electron impact in the gas source chamber of the device are from an external electrode plate (eg, item 11: FIG. 1B, FIG. 3 or FIG. 7) when actually used in a mass spectrometer. An output ion beam (eg, eg, item 10: FIG. 1B, FIG. 3 or 7) is accelerated from the source chamber through an ion exit slit (eg, item 10: FIG. 1B, FIG. 3 or FIG. 7) using a penetrating "pull-out" electric field that extends into the source chamber. Item 13: Form FIG. 1B, FIG. 3 or FIG. 7). A repulsive electrode plate (eg, item 8: FIG. 1B, FIG. 3 or FIG. 7) is typically provided, which directs a positive ion beam to the source chamber through a slit in the source chamber. It may also have applied a voltage that helps to repel it. These components of the Nier-type device have a specific position with respect to the ion exit slit in the source chamber, in which case it is desirable to produce the ions that form the ion beam.

[114] The more effectively the Nier-type source suppresses the area of analyte ionization in a smaller location, aligned with the exit slit and / or the repulsive electrode, the more effectively " A "pull-out" electric field (and / or repulsion electrode) is pulling out those ions. This is simply because the ions are less likely to "remove" the exit slit and hit the inner wall of the source chamber, which cannot contribute to the output ion beam. The intensity of the output ion beam is increased if the position of ionization in the source chamber can be controlled, and the ionized electrons are concentrated there.

[115] Moreover, when ions are generated in a highly separated region of a "pull-out" electric field, the energy they gain from being accelerated by that electric field varies in proportion to the degree of separation. This is not desirable as it reduces the resolution of the energy spectrum of the extracted ions. The better the Nier-type source suppresses the area of analysis ionization to smaller locations in the "pull-out" electric field, the smaller the energy range to pull out those ions (higher resolution).

[116] In the case of a new Nier-type source that combines an indirect thermionic source with an Einzel condensing lens and does not have a collimation magnetic field, the transmission of electrons through the entire device to the trap electrode, along with the collimating magnet, , It turned out to be significantly larger than the case of a conventional Nier type source with a direct heating coil filament without an Einzel lens. It should be noted that the application of a collimating magnetic field was found to actually reduce the electron transmission level. The magnetic field interferes with the Einzel lens's ability to focus the electron beam.

[117] The concentration and orientation of the electron emitters according to the present invention has increased the number of electrons transmitted through the trap electrode through the source chamber. The addition of an electrical ranging element between the electron emitter and the source chamber / enclosure, which acts as an Einzel lens, successfully focused the electron beam and increased electron transmission.

[118] As the electron beam intensity increases, the mass bias effect is reduced / eliminated by removing the collimating magnetic field from the ionized region in the source chamber. Focusing of the electron beam makes it possible to position the electron emitting surface even further away from the source chamber / housing. This, coupled with the lower operating temperature of the electron source, allows a reduction in heating effect to occur in the source chamber / enclosure, thereby reducing outgassing of pollutants.

[119] Although a few preferred embodiments of the invention have been shown and described, various modifications and modifications are made without departing from the scope of the invention, as defined in the appended claims. It will be understood by those skilled in the art that it can be done.

[120] Attention is paid to and all such articles and documents filed at the same time as or prior to this specification in connection with this application and which accept public access of this specification. The contents of various articles and documents are incorporated herein by reference.

[121] All of the features disclosed herein (including any accompanying claims, abstracts and drawings) and / or all of the steps of any method or process so disclosed. Any combination can be combined, except for combinations in which at least some of such features and / or steps are mutually exclusive.

[122] Each feature disclosed herein, including any accompanying claims, abstracts and drawings, has the same, equivalent or similar purpose, unless expressly provided otherwise. It can be replaced with a suitable alternative feature. Therefore, unless expressly specified otherwise, each disclosed feature is merely an example of a generic series of equivalent or similar features.

[123] The present invention is not limited to the details of the aforementioned embodiments (s). The present invention is any novel one, or any new combination of features disclosed herein (including any accompanying claims, abstracts and drawings), or so disclosed. It extends to any new one or any new combination of steps in any method or process.

Claims (16)

An electron source in a gas source mass spectrometer
An electron emitting cathode that communicates with the gas source chamber of the gas source mass spectrometer and presents a thermionic emission surface to provide electrons to it.
It is electrically isolated from the electron emitting cathode and radiates sufficient heat to the electron emitting cathode to be heated by the current in it and to thermionically release electrons from the electron emitting surface. An electron source comprising a heating element arranged so as to provide a source of electrons for use in ionizing the gas in the gas source chamber. The gas source mass spectrometer traverses the gas source chamber with a current of at least 0.5 mA in response to the electron emitting cathode being heated by the heating element to a temperature of 2000 ° C. or lower. The electron source according to claim 1, further comprising an electron trap that can operate to receive from an electron emitting cathode. Electrons are emitted from the electron emitting cathode at an electron input opening formed so as to form an electron beam in the gas source chamber, in which the gas source chamber is directed toward the electron trap without using a collimeter magnet. The electronic source according to claim 2, which is arranged to receive. The electron according to claim 2 or 3, wherein the electron emitting cathode can operate so as to be heated to a temperature of 2000 ° C. or lower by the heating element when the power input to the heating element does not exceed 5 W. source. The electron source according to any one of claims 1 to 4, wherein the electron emitting cathode is selected from an oxide cathode, an I cathode, or a Ba-impregnated cathode. The electron source according to any one of claims 1 to 5, wherein the electron emitting cathode comprises a base carrying a coating of a thermionic emitting material that presents the electron emitting surface. The electron source according to claim 6, wherein the coating comprises a material selected from alkaline soil oxides, osmium (Os), ruthenium (Ru). The electron source according to claim 6, wherein the base comprises tungsten or nickel. The electron source according to claim 8, wherein the base comprises tungsten impregnated with a compound containing barium oxide (BaO). The electron source according to any one of claims 6 to 9, wherein the base is a metallic material that separates the coating from the heating element. The electron source according to any one of claims 1 to 10, further comprising a sleeve surrounding the heating element and having the electron emitting surface at the end of the sleeve. The electron source according to any one of claims 1 to 11, wherein the heating element comprises a metal filament coated with a coating comprising a metal oxide material. A gas ion source for a mass spectrometer comprising the electron source according to any one of claims 1 to 12. The gas ion source according to claim 13, wherein the ion source is a Nier type gas ion source. A mass spectrometer comprising the gas ion source according to claim 13 or 14. The mass spectrometer according to claim 15, which is configured as a Nier type mass spectrometer.